MUNMAP(2) BSD System Calls Manual MUNMAP(2)
NAMEmunmap -- remove a mapping
SYNOPSIS#include<sys/mman.h>intmunmap(void*addr, size_tlen);
DESCRIPTION
The munmap() system call deletes the mappings for the specified address range, causing further refer-ences references
ences to addresses within the range to generate invalid memory references.
DIRTYPAGEHANDLING
How munmap() handles a dirty page, depends on what type of memory is being unmapped:
[Anonymous] If the memory is anonymous memory and if the last reference is going away, then the
contents are discarded by definition of anonymous memory.
[System V Shared] If the memory mapping was created using System V shared memory, then the contents
persist until the System V memory region is destroyed or the system is rebooted.
[File mapping] If the mapping maps data from a file (MAP_SHARED), then the memory will eventually
be written back to disk if it's dirty. This will happen automatically at some point
in the future (implementation dependent). Note: to force the memory to be written
back to the disk, use msync(2).
If there are still other references to the memory when the munmap is done, then nothing is done to the
memory itself and it may be swapped out if need be. The memory will continue to persist until the last
reference goes away (except for System V shared memory in which case, see above).
RETURNVALUES
Upon successful completion, munmap returns zero. Otherwise, a value of -1 is returned and errno is set
to indicate the error.
ERRORSMunmap() will fail if:
[EINVAL] The addr parameter was not page aligned (i.e., a multiple of the page size).
[EINVAL] The len parameter was negative or zero.
[EINVAL] Some part of the region being unmapped is not part of the currently valid address
space.
LEGACYSYNOPSIS#include<sys/types.h>#include<sys/mman.h>
The include file <sys/types.h> is necessary.
intmunmap(caddr_taddr, size_tlen);
The type of addr has changed.
SEEALSOgetpagesize(3), msync(2), munmap(2), mprotect(2), madvise(2), mincore(2), compat(5)HISTORY
The munmap() function first appeared in 4.4BSD.
BSD October 16, 2008 BSD

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